Various processes to make cyclic alkylene ureas have been described in the literature and in patents, such as in J. Org. Chem. 1950, vol. 15, pages 471 to 474, and 475 to 480, relating to the synthesis of ethylene urea from urea and ethylenediamine, and from ethylene glycol or ethanolamine and urea, or carbon dioxide and ammonia.
As early as 1886, E. Fischer and H. Koch reported in Annalen, vol. 232, page 227 (1886), the preparation of ethylene urea by heating ethylenediamine and diethyl carbonate at 180° C. As described therein, this reaction was carried out in a sealed tube and required the use of high temperature.
In U.S. Pat. Nos. 2,436,311, 2,504,431, 2,526,757, as well as in the patent publication US 2010/0261015 A1, a process is disclosed for the manufacture of ethylene urea by the reaction of 1,2-ethylenediamine with urea, wherein these two starting materials are mixed and heated to a temperature of at least from 240° C. to 260° C. As described in these patents, this reaction appears to proceed through a series of stages at temperature between 100° C. and 260° C. at atmospheric or elevated pressure. Release of ammonia, a by-product of this reaction, begins as the reaction mixture reaches 100° C. to 115° C. This reaction is carried to completion by continued heating usually to an end temperature of from 170° C. to 240° C. According to these prior art references the reaction can be carried out under anhydrous conditions or in presence of water and/or a high boiling solvent such as ethylene glycol and diethylene glycol, however, the beneficial use of water in markedly increasing the yield versus reactions conducted under anhydrous conditions is noted and exemplified. Water is believed to be responsible for the more complete conversion of the intermediate condensation product to ethylene urea. The crude ethylene urea thus formed does not form a clear solution in water but results in turbid solutions which are distinctly alkaline, while pure ethylene urea is fully soluble in water. The desired product ethylene urea is generally isolated from the aqueous solution by crystallisation as hemihydrate, and comprises a mass fraction from about 5% to 15% of water. Some of the disadvantages of this process route using urea as a reactant are the formation of water-insoluble by-products, the need to react at higher temperature and higher pressure conditions, and formation of hydrated ethylene urea which is not a free-flowing powder, but has a propensity to cake and form lumps.
Other processes using organic carbonates as a reactant include the previously disclosed reaction (U.S. Pat. No. 2,892,843) of cyclic 1,2-alkylene carbonates, namely ethylene carbonate or propylene carbonate, with ammonia at temperatures of from 200° C. to 290° C., and autogenous pressure.
A recent journal article in Applied Catalysis A: General 341 (2008), pages 133 to 138, describes the synthesis of 2-imidazolidinones via the trans-esterification of equal amounts of substance of ethylene carbonate and a diaminoalkane using a heterogeneous basic metal oxide catalyst like magnesium oxide, MgO.